Well warmer boys and girls, you have a fine experiment there, but alas, it doesn't demonstrate what the fraud doing the experiment claimed. Either he is a deliberate fraud, or not qualified to be teaching physics.
That experiment provides a fine example of the heat of compression, not warming due to CO2. If he filled his tank with any gas that was heavier than air, the temperature in the tank would have gone up. The temperature increase was due to a phenomenon known as the heat of compression. It is a very well known and understood property of gasses. The thermal energy of a gas increases when it is compressed, even just a little. When you confine a gas in an enclosed space, and heat it, you observe the heat of compression.
Had the "professor" put a tube in the tank with the CO2 through the lid so that the pressure could equalize, (since CO2 is heavier than air it wouldn't have escaped) or put a sensor in the tank to monitor the change in pressure to keep the experiment honest, the claim of warming due to CO2 would not have been made. CO2 does not, can not, and never has caused warming due to anything like the so called greenhouse effect.